A man dressed as Japanese imperial army soldier and a man wearing a rising sun flag headband stand behind a rising sun flag in front of Yasukuni Shrine on the anniversary of Japan's surrender in World War Two in Tokyo, Japan, on Monday.

Relations between Japan and South Korea simmered Monday on the 71st anniversary of the end of World War II.

Dozens of Japanese lawmakers visited the Yasukuni Shrine in Tokyo, which honors all who died for the Japanese Empire, including more than 1,000 World War II-era war criminals. Meanwhile, a group of South Korean lawmakers also deliberately chose Monday to land on an island in the Sea of Japan, celebrating the country’s liberation from 35 years of Japanese colonization in the first half of the 20th century. South Korea controls the islands, although Japan lays claim to them.

The controversies on the war anniversary underscore the continuous tension over Japan’s reluctance to apologize for or acknowledge 20th century history the way South Korea or China insist they should.

“History is the core concern of Northeast Asian politics,” Park Joon-woo, a retired adviser to South Korean President Park Geun-hye, told Peter Ford of The Christian Science Monitor last July. “And that will continue as long as Japanese leaders try to erase their history.”

This disagreement over the past has reverberated into the present in Asia and across the world, wrote Mr. Ford.

Seventy years after the end of the war in the Pacific, Japan’s neighbors say they are still waiting for an apology they can believe is a sincere expression of Japan’s national feeling about the old Imperial Army’s invasions and the atrocities it committed. Japanese Prime Minister Shinzo Abe is showing no signs he is ready to express the type of contrition that some of his predecessors have voiced in the past. The ramifications of this are now reverberating around the globe.

What might seem to much of the world like arcane disputes over incidents in 20th-century history are threatening Asia’s future and complicating the big power rivalry between the United States and China. They could strengthen Beijing’s standing in the region at the expense of Washington’s clout. They have poisoned relations between the publics and governments of America’s two closest Asian allies, Japan and South Korea, to the point where their leaders cannot meet.

Japanese Prime Minister Shinzo Abe refrained from visiting the Yasukuni Shrine on Monday, an effort to not draw anger from South Korea and China, as he did when he visited the shrine in 2013. South Korea and China view the shrine as a reminder of Japanese militarism and wartime atrocities. Mr. Abe instead sent the shrine a ritual offering, which was delivered in his name by Yasutoshi Nishimura, an aide in Abe’s Liberal Democratic Party (LDP).

The offering still drew criticism from Seoul.

"(We) express deep concern and regret that responsible political leaders ... are again paying tribute to the Yasukuni Shrine that glorifies the history of the war of aggression," South Korea's Ministry of Foreign Affairs said in a statement.

One past wartime wound that remains raw for South Korea is the fate of “comfort women,” Korean women and girls forced to work as prostitutes in Japan’s wartime military brothels.

Past Japanese leaders apologized dozens of times “from remorse and regret to sorrow and repentance” for their country’s behavior, writes Ford. The most direct statement came in 1995, when then-Prime Minister Tomiichi Murayama acknowledged Tokyo’s history of “colonial rule and aggression” and offered his “heartfelt apology” for “these irrefutable facts of history.” At the time, South Korea and China accepted the apologies.

However, the two countries have since become disturbed at what they consider a lack of sincerity from some in Tokyo. Most infuriating to them was Abe’s visit to the Yasukuni Shrine in 2013, a visit he has not repeated.

“Abe finds ways of signaling to his domestic audience” what he thinks, said Boston University political scientist Thomas Berger, author of “War, Guilt, and World Politics After World War II,” and “nobody has any doubts where he stands.”

Japanese Emperor Akihito contrasted Abe Monday by reiterating his “feelings of deep remorse” for the conflict, a phrase he used last year. Some saw his remarks as a subtle rebuke of Abe’s less apologetic tone, according to Reuters.